The present invention relates to an exposure apparatus and exposure method for irradiating the surface of a photosensitive material with light in accordance with an exposure pattern and forming a desired pattern shape on the material. The invention is also directed to a method for manufacturing of a wiring board that uses the exposure method.
With the proliferation of multi-item and variable-lot-sized production in the manufacture of wiring boards, there is an expectation that it will be possible not only to shorten order-to-delivery cycle time for such production, but also to supply highly accurate wiring at lower prices. Under these circumstances, there is a strong demand for an innovative manufacturing technology that enables multi-item and variable-lot-sized production, high accuracy, and cost reduction to be realized simultaneously.
Forming a pattern on a printed-wiring board or the like by using a conventional technique has been accomplished by coating a photosensitive liquid resist or dry film resist on the board, and exposing via a photomask after the coating, then developing, etching, plating, and other processes.
Instead of the above conventional technique, a maskless direct exposure technique using an ultraviolet light or a visible light emitted from an argon ion laser or any other gas laser as a light source was later introduced in the 1990s. In this maskless direct exposure technique, making photomasks is not required. Thus, this exposure technique makes it possible not only to save mask-manufacturing equipment costs and material costs significantly, but also to reduce the time (lead time) for mask-making to manufacture boards. Since the maskless direct exposure technique also features highly accurate position alignment, it is considered as a technique that improves manufacturing processes such as printed-wiring board or semiconductor package.
It is proposed to use a semiconductor laser diode as a light source for the maskless direct exposure technique, instead of a gas laser. Gas lasers have difficulties with maintenance, including the need to supply a process gas.
Japanese Laid-Open Patent Publication No. 2004-85728 (Patent Reference 1) describes a maskless direct exposure method which employs a semiconductor laser light source to directly expose a photosensitive resin that contains an infrared absorption dye using a laser beam with a wavelength between 750 nm and 1200 nm.
In addition, Japanese Laid-Open Patent Publication No. 2004-39871 (Patent Reference 2) describes an exposure apparatus that uses a semiconductor laser as its exposure light source to emit blue-violet light whose wavelength is in the vicinity of 408 nm.
As a proposal to improve those exposure light sources, a method using a two-dimensional optical modulator to increase an imaging speed is known. The method is described in Japanese Laid-Open Patent Publication No. 2003-15077 (Patent Reference 3) and the like, in lieu of the laser beam scanning optical system including a polygonal mirror and f-θ lens optics. The two-dimensional optical modulator is a device that uses pixel-by-pixel digital on/off control to realize two-dimensional imaging. Typical examples of the two-dimensional optical modulator are a liquid-crystal panel and a digital micromirror device (DMD). Patent Reference 3 mentioned above also describes a maskless direct exposure apparatus including an ultraviolet (UV) light source, a slit, a DMD, imaging optics, and other elements. In addition, Patent Reference 3 discusses the driving principles of the DMD and the deterioration of the DMD in life due to UV light irradiation.
With respect to two-dimensional imaging that is a feature of such two-dimensional optical modulation, increasing the intensity of light allows the imaging speed to be further increased. Optics that increases light intensity is proposed in Japanese Laid-Open Patent Publications No. 2002-182157 (Patent Reference 4) and 2004-157219 (Patent Reference 5).